1. Field of the Invention
The present invention relates to benzoxazolyl optical brightners, and more particularly relates to benzoxazolyl optical brightners and thermoplastic compositions containing benzoxazolyl optical brightners.
2. Description of the Related Art
Organic phosphite stabilizers have been previously used to stabilize various thermoplastic compositions, including polyolefins, aromatic polycarbonates, and polyesters. For example, Horn, Jr., U.S. Pat. No. 4,385,145, issued May 24, 1983, discloses utilizing from about 0.05 to about 1.0 percent by weight pentaerythritol diphosphite ester as a stabilizer for poly(alkylene terephthalate); and Axelrod, U.S. Pat. No. 4,066,611, discloses a stabilized aromatic polycarbenate composition containing small proportions of bis(2,4-ditertiarybutylphenyl)pentaerythritol diphosphite and an epoxy compound. The utilization of phosphite aromatic stabilizers in polycarbonate resin can reduce the generation of yellow degradation products, but degradation of the phosphite product into phosphoric acid during extended exposure of the thermoplastic resin to moisture at an elevated temperature can result in an increase in hazing in the composition. Additionally, utilization of 2,2'-(2,5-thiophenediyl)bis(5-tertbutylbenzoxazole) as an optical brightner for polycarbonate resins has been disclosed in Federal Register Volume 53, No. 87, Friday, May 4, 1990, page 18721-18722. Product literature set out for Optiblanc PL by 3V Sigma sets out that benzoxazole,2,2'-(2,5-thiophendlyl)-bis(5-(1,1-dimethylethyl)(or 2,5-bis(5-tertbutylbenzoxazole-2-yl)thiophene) is useful as a fluorescent whitening agent for thermoplastic materials, and sets out that for nonpigmented thermoplastics it is efficient to add small quantifies of the compound in order to compensate for the "yellow" color of the substrate, with recommended additive levels being between 0.001 and 0.05 percent, and further setting out that in the case of thermoplastic with white pigments and in particular in case of pigmentation with titanium dioxide, the recommended addition levels are between 0.01 to 0.2 percent, and that there is a possibility to combine the fluorescent whiting agent with bluing materials.
Accordingly, an object of the present invention is to provide thermoplastic compositions with reduced level of phosphite stabilizer, which exhibit low yellowness levels, which preferably exhibit bright natural color, and which is more preferably transparent.